Phosphorus leaching change point of subtropical variable-charge soils and its relations with soil properties
亚热带可变电荷土壤磷素淋失临界点及其与土壤特性的关系

This study was to understand the characteristics of the P leaching potential of variable-charge soils and to evaluate their P leaching risks.Sixteen soils which were representatives of variable-charge soils in subtropical China, as determined by their phosphorus (P) leaching change point (the soil P concentration where P moves from soil to water), were collected.Basic properties e.g.pH, CEC, clay and organic matter, exchangeable Ca2+ and Mg2+, Fe2O3 and Al2O3 concentrations were determined.There were large variations in Olsen P concentrations (56~123 mg·kg-1) at the P leaching change points.The Olsen P concentrations of upland soils were mainly quite small (< 60 mg·kg-1) and were considerably higher in paddy soils (> 80 mg·kg-1).Therefore the P leaching potential was lower in the paddy soils than in the upland soils.Principal Component Analysis indicated that soil chemical properties can produce both positive and negative effects on Olsen P concentration.This explains why linear correlations between Olsen P concentrations and single soil chemical properties are generally non-significant. Such analyses cannot realistically reflect the effects of pH, CEC, and the concentrations of clay, exchangeable Ca2+ and Mg2+ (no significant correlations), and even give contradictory results with Fe2O3 and Al2O3 (negative correlations).Olsen P concentrations at the change points of the variable charge soils were higher than the commonly measured in permanent-charge soils.Because the Olsen-P concentrations in all of the variable charge soils were considerably less than the Olsen P concentrations at the change point, it is suggested that potential risks of P leaching from variable-charge soils are small in subtropical China.